1. Field of the Invention
The present invention relates to a method and apparatus for handling uplink transmission start in a wireless communications system, and more particularly to a method and related apparatus for reducing signaling overhead and avoiding radio resource waste.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting third generation mobile telecommunication technology, the prior art provides High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), which are used to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
HSUPA increases upstream network performance, reduces transmission delay by rapid retransmission of erroneous data transmissions, and can adjust transmission rate based on channel quality. To realize this type of “power control,” HSUPA adopts technologies such as NodeB Scheduling, Hybrid Automatic Repeat Request (HARQ), Soft Handover, and Short Frame Transmission. Correspondingly, the 3rd Generation Partnership Project (3GPP) defines an Enhanced Dedicated Transport Channel (E-DCH) for controlling operations of HSUPA. E-DCH introduces new physical layer channels, such as E-HICH, E-RGCH, E-AGCH, E-DPCCH, and E-DPDCH, which are used for transmitting HARQ ACK/NACK, Uplink Scheduling Information, Control Plane information, and User Plane information. Detailed definitions of the above can be found in the Medium Access Control (MAC) protocol specification, “3GPP TS 25.321 V6.7.0,” and are not given here.
Through NodeB Scheduling technology, a base station (Node B) is allowed to adjust transmission power of mobiles or user equipments (UEs) within its transmission range (cell), so as to control uplink transmission rate of the mobiles. Referring to sections 9.2.5.2.1 and 9.2.5.2.2 of the aforementioned MAC protocol specification, the network can provide Relative Grant (RG) messages and Absolute Grant (AG) messages to a mobile through an E-DCH Relative Grant Channel (E-RGCH) and an E-DCH Absolute Grant Channel (E-AGCH) respectively, so as to adjust the transmission grant of the mobile. The E-AGCH is a shared channel that use an E-DCH Radio Network Temporary Identifier (E-RNTI) in order to address the AG messages to specific mobiles. The AG messages are used to directly adjust the transmission grant of mobiles, and can be classified into two types, Primary and Secondary. The Primary AG message provides an uplink resource grant for a specified mobile served by a cell. The Secondary AG message provides an uplink resource grant for a group of mobiles served by the cell, so as to reduce signaling overhead. On the other hand, the AG message includes an AG value field and an AG scope field. The AG value field indicates the transmission resource the mobile is allowed to use in the next transmission. The AG scope field indicates that the applicability of the AG value is “Per HARQ process” or “All HARQ Processes,” meaning whether the AG value field will affect one or all HARQ processes.
According to section 11.8.1.3.1 of the aforementioned MAC protocol specification, after a mobile receives an AG message, if the E-RNTI type is “Primary,” the AG value is set to “INACTIVE,” the AG scope is “Per HARQ process,” and a 2 ms TTI is configured, then the mobile shall de-activate a current HARQ process, which is the process identified by the value of a variable CURRENT_HARQ_PROCESS. If the E-RNTI type is “Primary,” the AG value is set to “INACTIVE,” the AG scope is “All HARQ processes,” and a secondary E-RNTI was configured by higher layers, then the mobile shall activate all HARQ processes, set Serving Grant (SG) value to stored secondary grant (Serving_Grant=Stored_Secondary_Grant), and set a primary grant state variable to “none” (Primary_Grant_Available=false), meaning that the SG value can be affected by Secondary AG messages.
Besides, if the AG value is different from “INACTIVE,” and the E-RNTI type is “Secondary,” then the mobile shall set the variable Stored_Secondary_Grant to the AG value. Oppositely, if the E-RNTI type is “Primary” or the variable Primary_Grant_Available is set to “False,” then the mobile shall set the SG value to the AG value (Serving_Grant=AG value). Note that, definitions of “INACTIVE,” “Stored_Secondary_Grant,” “Primary_Grant_Available,” and “Serving_Grant” can be found in section 3.1.2 of the aforementioned MAC protocol specification.
Therefore, when the Primary AG message sets the AG value to “INACTIVE” and the AG Scope indicates “Per HARQ process” while a 2 ms TTI is configured, the prior art simply de-activates the corresponding HARQ process and keeps the variable Primary_Grant_Available unchanged. The variable Primary_Grant_Available represents whether the SG value is only affected by the Primary AG and RG messages. If Primary_Grant_Available=“True,” the SG value is only affected by the Primary AG or RG messages. If Primary_Grant_Available=“False,” the SG value is affected by the Primary AG, Secondary AG, or RG messages.
In addition, according to section 11.8.1.3.1 of the aforementioned MAC protocol specification, when E-DCH transmission is started (a variable E_DCH_TRANSMISSION is set to “True” from “False”), the mobile shall activate all HARQ processes. At the same time, if the upper layer (Radio Resource Control, RRC) has provided an IE “Serving Grant,” which contains IE's “Serving Grant value” and “Primary/Secondary Grant Selector,” the mobile shall set the variables Serving_Grant and Primary_Grant_Available accordingly. Oppositely, if the IE “Serving Grant” is not provided, the mobile shall set the variable Serving_Grant to a parameter Zero_Grant to indicate that the SG value of the mobile is 0, and set the variable Primary_Grant_Available to “True” to indicate that the SG value is being affected by the Primary AG messages, and thus the SG value is not affected by the Secondary AG messages.
Therefore, by the prior art, when E-DCH transmission is started, if the IE “Serving Grant” is not provided, the variable Primary_Grant_Available is set to “True,” and the SG value of the mobile is not affected by any Secondary AG message. Under such circumstance, the SG value will keep to be the parameter Zero_Grant unless a Primary AG message is received, and Secondary AG messages will not be able to change the SG value from Zero_Grant to a new value. In other words, the only way to grant HARQ processes of the mobile to transmit data is through the Primary AG messages. The advantage of the Secondary AG messages vanishes, and signaling overhead is increased.